Numerical Simulation And Experiments On Drag Reduction Characteristics In Groove Surface

In recent years, the drag reduction induced from turbulent boundary layer has become an important area of fluid dynamics research. As a practical and efficient energy-saving technology, turbulent boundary layer drag reduction method has more and more received attention. Shark skin surface is covered with special grooves along the flow direction, which is believed to be able to reduce the drag resistance in swimming. Inspired by this, several different shapes of grooved surfaces were simulated and studied for their drag reduction characteristics in this paper.This thesis analyzes the drag reductions of several different types of V-grooved surfaces (tip angle53°,45°,60°,75°and90°) under the condition of different Reynolds number respectively. We obtained the relationship between drag reduction rate and s+(s+=suT/u, where s+is the dimensionless spacing of riblets, s is the dimensional riblet spacing, uτ is the wall stress velocity, υ is the kinematic). It is found that tip angle75°V-grooved surface has the best drag reduction in V-grooved surfaces, when s+is15.4, giving the maximum drag reduction6.38%. However, through careful observation, it is found that the shark skin surface has more than one level of grooved rough surface. Inspired by this, a secondary micro-groove surface is designed by adding small-scale triangles on the top location of the53°V-grooved surface. When s+is28, the maximum drag reduction reaches8.07%for the two levels of micro-grooved surface. However, the maximum drag reduction rate is only3.69%for the first level grooved surface with a tip angle of53°. In addition, we also analyze drag reduction of L-grooved surfaces with the ratio of the riblet thickness to spacing t/s=0.04and0.02respectively. When s+is20, the maximum drag reduction is11.67%for L-grooved surface with t/s=0.02. When s+is18.58, the maximum drag reduction is9.19%for L-grooved surface with t/s=0.04.Finally, the drag reduction of V-grooved surface that assembled by a series of thin sharp blades is studied experimentally. By comparing the flow through the smooth channel and groove channel the drag reduction of V-grooved surface can be obtained. The experimental results show that when h+(h+=huT/u, where h+is the dimensionless height of riblet, h is the height of riblet) is24, the optimum drag reduction is4.65%.